A recent increase in performance and prevalence of electronic products is increasingly demanding efficient manufacture of a semiconductor device for these electronic products with an increase in integration scale (i.e., further miniaturization). For example, in a semiconductor exposure apparatus which transfers a circuit pattern onto a silicon wafer, the wavelength of exposure light has been shortened for micropatterning. More specifically, the exposure light has been changed to the KrF laser beam, ArF laser beam, F2 laser beam, soft X-ray radiated from an SR ring, and the like.
The exposure light with a short wavelength such as the F2 laser beam, and soft X-ray is greatly attenuated in the outer air. Thus, there is proposed a method of accommodating the exposure unit of an exposure apparatus in a chamber, and setting the interior of the chamber to an N2 atmosphere or reduced-pressure He atmosphere in which exposure light is less attenuated. In an electron beam exposure apparatus or the like, a vacuum atmosphere is formed. In a processing apparatus such as a CVD apparatus, an atmosphere different from the outer air or a vacuum atmosphere is formed, when a process gas different from the outer air is used or to prevent an organic substance or moisture from attaching to a substrate.
A conventional processing system typically comprises a load-lock chamber whose atmosphere can be switched between, for example, an atmospheric pressure environment and a reduced-pressure environment in transferring a substrate to be processed such as a semiconductor substrate, liquid crystal display substrate, or the like between a port serving as a supply portion and a process chamber which performs exposure processing or the like. The load-lock chamber has gate valves which connect to the port and process chamber, respectively. In the transfer of the substrate to be processed between the port and the load-lock chamber, the gate valve between the load-lock chamber and the process chamber is closed, and gas is supplied to the load-lock chamber or the load-lock chamber is opened to the outer air, thereby maintaining the pressure in the load-lock chamber at the atmospheric pressure. In the transfer of the substrate to be processed between the load-lock chamber and the process chamber, the gate valve between the load-lock chamber and the port is closed, and the load-lock chamber is evacuated to a vacuum, thereby maintaining the interior of the load-lock chamber in a vacuum or reduced pressure environment.
In general, when the pressure of gas abruptly drops, the temperature abruptly drops due to adiabatic expansion. In a conventional arrangement, evacuation of a load-lock chamber causes adiabatic expansion in the load-lock chamber, thus cooling the gas in the load-lock chamber. In the load-lock chamber, heat transfer from the walls of the load-lock chamber to the gas occurs in addition to the adiabatic expansion. An actual drop in gas temperature changes depending on the time required for gas exhaust. Generally, a temperature drop increases with an increasing gas exhaust rate.
For this reason, a conventional processing system cannot perform high-quality processing for a substrate to be processed while ensuring a predetermined throughput. The time required to evacuate a load-lock chamber affects not only the number of substrates to be processed that are supplied to a process chamber via the load-lock chamber per unit time but also the throughput of the processing system. Accordingly, the gas exhaust time is preferably short for the load-lock chamber. This is demanded particularly in a processing system such as an exposure apparatus which requires a high throughput.
However, a short gas exhaust time causes an abrupt drop in temperature of the atmosphere in the load-lock chamber. In, for example, a processing system which performs high-speed processing at a throughput of about 60 to 100 W/h, each load-lock chamber needs to be evacuated in several ten seconds for each wafer even if a plurality of load-lock chambers are provided. The volume of each load-lock chamber is preferably minimized in order to shorten the gas exhaust time. For example, the volume is usually designed to be 3 to 10 liters for a wafer having a diameter of 300 mm. When a load-lock chamber having a volume of 3 to 10 liters is evacuated in several ten seconds, the gas temperature drops by several ten degrees due to adiabatic expansion. According to experiments by the present inventor, when a load-lock having a volume of 8 liters and a room temperature of 23° C. is evacuated from the atmospheric pressure to 100 Pa, the temperature dropped to −25° C.
An abrupt drop in temperature in the atmosphere in the load-lock chamber causes condensation, and moisture condenses around fine particles, SO2, or the like in the gas. In the process of the condensation, moisture takes in fine particles present in the ambient space to form a large agglomeration of particles and moisture. Particles blown up by a flow of exhaust gas drop in an agglomerate state onto a substrate as the pressure of the exhaust gas decreases. The particles may contaminate the substrate or the moisture may attach to the substrate. It takes a long time to remove the adsorbed moisture, and a high throughput cannot be ensured. In addition, an oxide film may naturally grow on the surface of the moisture or a contaminant may dissolve in it, and thus, high-quality processing cannot be performed.